Deinking is the process of removing ink and other contaminants from waste paper. There are two main techniques in current use: "flotation" and "wash" deinking processes. In "flotation deinking" an aqueous suspension of waste paper pulp fibers, ink, and other non-cellulosic contaminants is formed and then air is mixed into the suspension. In the presence of appropriate additives, air bubbles selectively attach to ink particles and carry the particles to the surface of the aqueous suspension, thereby forming an ink rich froth. The froth is then removed, leaving behind a relatively ink-free fiber slurry. Flotation deinking processes are especially useful in removing hydrophobic inks with particle sizes larger than about 10 .mu.m. The additives used in such processes are generally specialty surfactants or fatty acid soaps, and/or combinations of the same which are intended to collect the detached ink particles and to agglomerate any relatively finer ink particles to increase removal efficiency in the flotation stage. The presence of additives that disperse the ink particles rather than agglomerate them is considered detrimental to the effectiveness of the flotation stage. "Wash deinking," on the other hand, is particularly useful when the ink and other particles being removed are finely dispersed so that the particles are smaller than about 5 .mu.m. This requires the addition of ink emulsifying surfactants/dispersants so that when a dilute waste paper pulp slurry is thickened, the fine inks will tend to stay with the water being removed rather than reattaching to the pulp fibers. Thus, a relatively clean pulp is produced.
Conventional methods for preparing alkaline earth metal tallates entail a one-step reaction of an alkaline earth metal hydroxide, e.g. calcium hydroxide, with tall oil fatty acids. Oftentimes, this has been done in situ during deinking by the addition of unneutralized tall oil fatty acids (TOFA) in the presence of water having high hardness, c.f. U.S. Pat. No. 5,417,807. In such a case, calcium salts are formed by reaction of the tall oil fatty acids with the calcium ions present in the hard water. When the water hardness was too low, additional calcium ions are provided by the addition of a salt such as calcium chloride to the water along with the tall oil fatty acids. Calcium salts of the fatty acid(s) provide a preferred bubble size/configuration for flotation.
Calcium stearate salts are known deinking agents which are usually prepared by combining calcium hydroxide and stearic acid under controlled conditions at a suitable temperature and mixing them in a high speed mixer.
Conventional preparative procedures, however, have failed to produce sufficiently effective deinking compositions from tall oil fatty acids. Specifically, conventionally prepared compositions from calcium hydroxide and tall oil fatty acids, i.e. calcium tallate dispersions, have heretofore suffered from one or more of the following problems: (i) they have not been stable for a commercially acceptable period of time; (ii) they have exhibited undesirable particle size distributions; and (iii) they have exhibited poor fluidity, i.e. upon aging the viscosity of the dispersions increases to a nonpumpable gel.
It is thus an object of the present invention to prepare an alkaline earth metal tallate having improved stability, desirable particle distributions, and good fluidity.